Microservice architecture is a trending topic in software design architecture and many enterprises adopted microservice design due its benefits and the rapid and wide deployment of cloud computing and as a result, many enterprises transformed their existing monolithic application to microservice to achieve business requirements as scaling up and agile development. In this paper we will guide software developers how to convert their existing monolithic application into microservice application without re-writing the whole microservice application from scratch, and we will also discuss the common issues that may face the software developer during the conversion processes. In addition to converting the business logic to microservice, we mention steps for converting the monolithic database into a database per service. Also, we summarize how Netflix and Airbnb converted their monolithic application to microservice application.